1. Field of the Invention
The present invention relates to a lens actuator mainly used for a camera and a mobile phone. The present invention also relates to a lens unit using the lens actuator and a method for manufacturing the lens unit.
2. Background Art
In recent years, electronic equipment, such as a camera and a mobile phone having a lens actuator with an auto-focusing function, has been put into widespread use. In response to such a trend, there has been growing demand for a lens actuator that offers simple assembly work and reliable performance. Here will be described a conventional lens actuator with reference to FIG. 6 and FIG. 7. FIG. 6 is a section view of a conventional lens actuator. FIG. 7 is an exploded perspective view of the lens actuator.
The lens actuator has carrier 1, cover 2, case 3, upper spring 4, lower spring 5, coil 6, yoke 7, a plurality of magnets 8, and spacer 10. Upper spring 4 and lower spring 5 are made of metallic thin plates. Carrier 1, cover 2, and case 3 are made of insulating resin. Carrier 1, which is formed into substantially a cylindrical shape, is situated between case 3 and cover 2 placed over the upper surface of case 3 so as to be movable in the vertical direction.
Upper spring 4 is disposed between the lower surface of cover 2 and the upper surface of carrier 1 in a slightly compressed condition. Lower spring 5 is disposed between the lower surface of carrier 1 and the inner bottom surface of case 3 in a slightly compressed condition. Upper spring 4 and lower spring 5 make a resilient contact with the upper surface and the lower surface, respectively, of carrier 1, thereby carrier 1 is held in a predetermined position.
Coil 6 is formed of a copper wire wound roundly. Coil 6 is fixed to flange 1A disposed at a lower section around the outer periphery of carrier 1. Yoke 7, which is made of iron or the like, is formed substantially in a cylindrical shape and has substantially a U-shape in section. Yoke 7 is disposed opposite to the outer periphery of carrier 1 so as to cover coil 6. The plurality of magnets 8, each of which has substantially an arc-shape, is attached on the inside wall of yoke 7.
The structure above forms a magnetic path from magnets 8 through yoke 7 and coil 6. Between the outer periphery of carrier 1 and yoke 7 and between coil 6 and magnets 8, predetermined clearances are formed for the movement of carrier 1 and coil 6 in the vertical direction.
Coil 6 has slack at its both ends for the vertical movement. Coil 6 is connected by soldering to electrodes 9, each of which is made of copper alloy or the like. The lower end of each of electrodes 9 downwardly protrudes from the bottom of case 3. Insulating resin-made spacer 10 is disposed above lower spring 5. The lens actuator is thus completed.
In the hollow section of carrier 1, screw-threaded groove 1B is formed so that the outer periphery of a lens barrel (not shown) is screwed therein, that is, the lens is fixed in carrier 1. The lens unit is thus structured. When the lens unit is mounted on electronic equipment, such as a camera and a mobile phone, electrodes 9 are connected to an electronic circuit (not shown) of the equipment via a lead wire, a connector or the like (not shown).
When a user operates a predetermined push button (not shown) of the equipment structured above, the electronic circuit of the equipment applies voltage to electrodes 9, thereby coil 6 carries electric current. Magnets 8 and yoke 7 form a magnetic field in the horizontal direction around coil 6. When electric current is flown into coil 6, coil 6 undergoes force perpendicular to the direction of the magnetic field, i.e., the force in the vertical direction. The force moves carrier 1 with coil 6 upward or downward, so that the focus of the lens mounted in carrier 1 is adjusted, i.e., the auto-focusing function is thus attained.
Upon the interruption of the current flow to coil 6, resilient force of upper spring 4 and lower spring 5 moves carrier 1 down to a predetermined position.
That is, upper spring 4 and lower spring 5 push the upper surface and the lower surface of carrier 1, respectively, so as to keep the lens barrel mounted in carrier 1 at a predetermined position. The application of voltage to coil 6 mounted on carrier 1 allows carrier 1 to move in the vertical direction. The auto-focusing function is thus attained.
As is described above, the lens actuator has the predetermined clearances between carrier 1 and yoke 7 and between coil 6 and magnets 8 so that carrier 1 is movable in the vertical direction. In the process of screwing the lens-equipped lens barrel into groove 1B, the screwing force inconveniently rotates carrier 1 due to the clearances and therefore the lens barrel is hard to be properly mounted therein. Therefore, the lens barrel has to be slowly screwed in groove 1B while carrier 1 is prevented from rotating by a wire-like tool. The manufacturing process needs extra time and effort.